<p>Sweating is not limited to hot and dry conditions. The sweat, in fact, is there always, but is perceived only on occasions when it drains out as perspiration. Not any more. Even unseen sweat can be sensed. Thanks to sophisticated electronics, tattoos and patches that can not only feel for sweat but also take a measure of its properties are on the anvil bringing in the vision of a wearable clinical laboratory. <br /><br />Sweat has been under the lens for decades for its qualities and effects on the human body. Investigations into what makes sweat reveal it to be a fluid playing a significant role in our daily life. Thanks to the biology of sweating, no matter the season, our body can always keep up a constant temperature. It is hard to see the sweat because it evaporates the instant it comes out. It is estimated that a human perspires about half-a-litre of sweat in a day. However, there is no certainty on the amount as collecting sweat is a tough task. <br /><br />Why do we need to know about sweat? Firstly, scientists consider it to be a window to our health as sweat is a watered-down form of urine. In a seminal study almost a century ago, a rubber technologist named H H Mosher diligently collected and studied blood, urine and sweat samples from volunteers.<br /><br />He found that unlike blood, sweat resembled urine in all its contents. Like urine, sweat is also acidic and tastes sour. It contains urea, uric acid, amino acids, sugar, minerals and creatinin, but in smaller proportions than in urine. The only difference being the presence of high amount of lactic acid. <br /><br />Easier ways to study perspiration<br /><br />The second reason is more of business. The similarity between urine and sweat is also the reason why we smell dirty after a heavy perspiration. Cosmetic products such as anti-perspirants survive on this fermenting property of the sweat. But collecting and analysing sweat is not an easy task. Mosher, for instance, collected sweat from volunteers by steaming them up in a hot chamber. The volunteers were covered with specially designed rubber sheets that drained all sweat perspired by the volunteers.<br /><br />However, as this procedure cannot be used on ailing individuals, scientists are looking for an easier method to collect and study sweat. One of the approaches has been to develop skin patches that sense specific contents of sweat. The sophistication achieved in analytical techniques has ensured that we no longer need bottles of sweat for testing. A swab is sufficient. This would be useful in sport and healthcare settings, there is a need for continuous, non-invasive monitoring of bio-markers to assess human performance and health . <br /><br />For sportspersons, loss of minerals is an important factor that affects their performance. Loss of minerals like sodium, iron and zinc can induce simple cramps to deadly heart attacks. Two years ago, Joseph Wang and colleagues at the University of California, San Diego, USA, developed a special nanosensor. Thin as a tattoo, it responds to zinc ions in the sweat. As one sweats, the sensor attached to an electronic reader provides information on the changes of zinc concentration in the body. Zinc is only one of the many components of sweat that scientists are interested in. <br /><br />Continuous monitoring of health<br /><br />For the clinicians, urea, lactic acid, sugars and creatine are the most important constituents of sweat. Their concentrations are indicators of underlying health conditions. Measuring them could provide a means of continuous monitoring of health. Salzitsa Anastasova and her colleagues at Imperial College London, UK have been looking into this problem. In a recent publication in the journal Biosensors and Bioelectronics, they have reported designing of a microfluidic skin patch that can measure lactate, sodium, pH (acidity) and cortisol simultaneously.<br /><br />Salzitsa’s invention looks like a cut-out of a clover leaf. Each of the four petals can sense one component. Thin membranes of polymers and iridium metal and paper are judiciously laid one over the other to create the patch. It bears on one of its face a mat of tiny needles — about 200 needles crowd together in just one millimetre space.<br /><br />The needles hold the patch on the skin and also suck up the sweat. Tiny canals in them lead the sweat to the sensors. Thus, the patch can give out readings non-stop as one works out on the treadmill or the cycle. Besides analysing the contents, the patch also can tell how fast the skin is getting hot or cold. All information were gathered via a bluetooth.<br /><br />The unobtrusive patches, the precision sensing and live reporting of the contents of sweat can be a boon for sportspersons as well as patients who need continuous monitoring of health conditions. Unlike urine testing or blood testing, the wearable sensors can do the job as and where the patient is.</p>
<p>Sweating is not limited to hot and dry conditions. The sweat, in fact, is there always, but is perceived only on occasions when it drains out as perspiration. Not any more. Even unseen sweat can be sensed. Thanks to sophisticated electronics, tattoos and patches that can not only feel for sweat but also take a measure of its properties are on the anvil bringing in the vision of a wearable clinical laboratory. <br /><br />Sweat has been under the lens for decades for its qualities and effects on the human body. Investigations into what makes sweat reveal it to be a fluid playing a significant role in our daily life. Thanks to the biology of sweating, no matter the season, our body can always keep up a constant temperature. It is hard to see the sweat because it evaporates the instant it comes out. It is estimated that a human perspires about half-a-litre of sweat in a day. However, there is no certainty on the amount as collecting sweat is a tough task. <br /><br />Why do we need to know about sweat? Firstly, scientists consider it to be a window to our health as sweat is a watered-down form of urine. In a seminal study almost a century ago, a rubber technologist named H H Mosher diligently collected and studied blood, urine and sweat samples from volunteers.<br /><br />He found that unlike blood, sweat resembled urine in all its contents. Like urine, sweat is also acidic and tastes sour. It contains urea, uric acid, amino acids, sugar, minerals and creatinin, but in smaller proportions than in urine. The only difference being the presence of high amount of lactic acid. <br /><br />Easier ways to study perspiration<br /><br />The second reason is more of business. The similarity between urine and sweat is also the reason why we smell dirty after a heavy perspiration. Cosmetic products such as anti-perspirants survive on this fermenting property of the sweat. But collecting and analysing sweat is not an easy task. Mosher, for instance, collected sweat from volunteers by steaming them up in a hot chamber. The volunteers were covered with specially designed rubber sheets that drained all sweat perspired by the volunteers.<br /><br />However, as this procedure cannot be used on ailing individuals, scientists are looking for an easier method to collect and study sweat. One of the approaches has been to develop skin patches that sense specific contents of sweat. The sophistication achieved in analytical techniques has ensured that we no longer need bottles of sweat for testing. A swab is sufficient. This would be useful in sport and healthcare settings, there is a need for continuous, non-invasive monitoring of bio-markers to assess human performance and health . <br /><br />For sportspersons, loss of minerals is an important factor that affects their performance. Loss of minerals like sodium, iron and zinc can induce simple cramps to deadly heart attacks. Two years ago, Joseph Wang and colleagues at the University of California, San Diego, USA, developed a special nanosensor. Thin as a tattoo, it responds to zinc ions in the sweat. As one sweats, the sensor attached to an electronic reader provides information on the changes of zinc concentration in the body. Zinc is only one of the many components of sweat that scientists are interested in. <br /><br />Continuous monitoring of health<br /><br />For the clinicians, urea, lactic acid, sugars and creatine are the most important constituents of sweat. Their concentrations are indicators of underlying health conditions. Measuring them could provide a means of continuous monitoring of health. Salzitsa Anastasova and her colleagues at Imperial College London, UK have been looking into this problem. In a recent publication in the journal Biosensors and Bioelectronics, they have reported designing of a microfluidic skin patch that can measure lactate, sodium, pH (acidity) and cortisol simultaneously.<br /><br />Salzitsa’s invention looks like a cut-out of a clover leaf. Each of the four petals can sense one component. Thin membranes of polymers and iridium metal and paper are judiciously laid one over the other to create the patch. It bears on one of its face a mat of tiny needles — about 200 needles crowd together in just one millimetre space.<br /><br />The needles hold the patch on the skin and also suck up the sweat. Tiny canals in them lead the sweat to the sensors. Thus, the patch can give out readings non-stop as one works out on the treadmill or the cycle. Besides analysing the contents, the patch also can tell how fast the skin is getting hot or cold. All information were gathered via a bluetooth.<br /><br />The unobtrusive patches, the precision sensing and live reporting of the contents of sweat can be a boon for sportspersons as well as patients who need continuous monitoring of health conditions. Unlike urine testing or blood testing, the wearable sensors can do the job as and where the patient is.</p>
